It is often necessary to drill or form core holes in concrete floor slabs. For example, it may be necessary to carry out repairs on conduits in the slabs or to carry out inspections. It can be difficult to repair the holes afterwards. Various forms of shuttering can be used together with a settable material. However, the result tends to be unsightly. Furthermore, the settable material and the concrete of the slab are generally not homogenous once the settable material has set in the hole. Thus, a plug of the material can be pushed out of the hole and fall onto the floor below. This might happen when a vehicle or some other bad passes over the hole.